JERUSALEM (AFP) - The Israeli air force hit more than 300 Hamas targets in the Gaza Strip overnight in response to rocket fire from the besieged Palestinian territory, an army spokesman said on Thursday.

"We aimed at 322 targets in Gaza overnight, taking to 750 the total number of Hamas targets hit by the army since the start (on Tuesday) of Operation Protective Edge," Lieutenant Colonel Peter Lerner told journalists in a telephone conference.

Among the targets hit were rocket-launching sites of Hamas's armed wing the Ezzedine al-Qassam Brigades, as well as tunnels used by the group and Hamas command posts, Lerner said.

He warned that a ground assault was still being considered.

"More than 20,000 reservists have been recruited but a ground assault would be the last option if we judge it necessary," he said.

Israel's cabinet has authorised the call-up of 40,000 reservists for such an operation, which looks increasingly likely as the conflict drags on, commentators say.

The army says Gaza militants have fired some 300 rockets at Israel since the Jewish state began Operation Protective Edge to stamp out the rocket fire.

Several of those have landed or been intercepted near Jerusalem, Tel Aviv and the northern city of Hadera.

Israeli air strikes have killed at least 70 people since the operation began, including at least 11 women and 18 children, according to medical reports.